This invention relates to a disk brake mounted on a motor vehicle, and more particularly a disk brake which is less likely to squeak during braking either while the car is moving forward or backward by improving the way in which the braking torque to the pads is borne. The terms "disk-leading side" and "disk-trailing side" herein used refer to the sides of the caliper at which the disk enter and exits the caliper, respectively, while the car is moving forward.
A disk brake of the type is known in which the pads to be brought into frictional contact with the disk are mounted so as be slidable in the axial direction of the disk between guide portions provided opposite to each other at the disk-leading and disk-trailing sides of the torque member or the caliper, and in which lugs at both ends of the back plates of the pads are engaged with guide grooves or protrusions of the guide portions to restrict the rotation of the pads, and the braking torque applied to the pads is borne by torque-bearing portions of the torque member or the caliper. A structure is proposed which can effectively suppress squeaking in unexamined Japanese patent publication 8-135696.
In this structure, as shown in FIG. 5, liners 11 are fitted in the guide portions 3 of the torque member 2 to urge the pads 1 radially outwardly with an arm 12 of the liner 11 at the disk-leading side and urge the pads 1 radially inwardly with an arm 12 of the liner 11 at the disk-trailing side. The torque-bearing portions 3a at the disk-leading and disk-trailing sides are located on the radially inner side (i.e. the side including the center of the disk) of the tangential line L of the disk that passes the center O of the brake cylinder (that is, center of pressing).
In the arrangement of FIG. 5, when the brake is applied while the car is moving forward, angular moment Ml produced by component forces Fay, Fby of the braking forces Fa and Fb applied to the disk at the disk-leading and disk-trailing sides, angular moment M2 produced when the center of the reaction force Fd shifts toward the center of the disk from the center of the tangential force Fc (which acts in the tangential direction of the disk) (this center is on the center of pressing O), and angular moment M3 produced by component forces fay, fby of the spring forces fa, fb of the resilient arms 12 are applied to the pads 1. The moments M1, M2, M3 are all counterclockwise. Thus, when the brake is applied while the car is traveling forward, the pads are prevented from pivoting. This effectively suppresses squeaking.
But when the brake is applied while the car is backing, the angular moments M1 and M2 act clockwise, while the moment M2 remains counterclockwise. Thus, when the combined force of the moments M1 and M2 overcomes the moment M3, the pads 1 may move, triggering vibrations of the pads 1. The brake thus begins to squeak. With a floating type disk brake of a type having its caliper 5 supported so as to be slidable in the axial direction of the disk by slide pins 7 (see FIG. 1), pin clearances are present at the caliper guide portions. But the pads move and the pin clearances disappear before predetermined torque-bearing portions are reached, so that the braking torque is borne by the pins. As a result, the line for bearing braking torque tends to become unstable. The brake thus tends to squeak. Thus, higher squeak-preventive effects are required for floating type disk brakes.
If the pad biasing directions at the disk-leading and disk-trailing sides were reversed from the illustrated arrangement to stop the movement of the pads during backward-travel braking, squeak-preventive effects during forward-travel braking which is more important would weaken. Thus, such an arrangement cannot be adopted.
An object of this invention is to increase the squeak preventive effects during backward-travel braking without sacrificing the squeak preventive effects during forward-travel braking.